As a technique of manufacturing an orifice plate, press shearing, wherein a material to be processed is die-cut in a given dimension, is known. In general press shearing, a cut end surface includes shear drop 3, sheared surface 4, fracture surface 5, and burr 6. Conventional press shearing has problems such as “large shear drop and large burr,” “large fracture surface and small sheared surface,” and “sheared surface and fracture surfaces not on a same plane.” If orifice plates for injecting liquids, etc. are manufactured by the known processing method described above, these problems may cause flow rate fluctuations in the orifice plates.
As a shearing method to ensure precision punching allowing little or no shear drop 3 or fracture surface 5 on the cut end surface of a material having undergone press shearing, shaving and fine blanking methods are generally known.
In a shaving method, as disclosed in Patent Literature 1, for example, punching is performed in advance in a dimension and shape including a shaving allowance (rough punching), and then the shaving allowance only is die-cut accurately in the shaving process. In the shaving process, by performing shaving once to several times depending on the degree of difficulty and desired precision of the processing, a cut end surface with little shear drop 3 and fracture surface 5, and a large and smooth sheared surface 4 is obtained. However, since the number of times of shaving processes must be increased and more precise dies are needed, production cost increases. Furthermore, the number of working processes increases, and the die accuracy must be improved.
In a fine blanking method, as disclosed in Patent Literature 2, for example, by creating a protrusion in a work-supporting section and minimizing the clearance between a punch and a die, high compression stress is generated within a material, which increases the ductility of the material, thus delaying generation of cracks. The fine blanking method can produce a clear cut end surface having small shear drop 3 and small fracture surface 5, and a large, and smooth sheared surface 4. However, due to high accuracy required for the punch and the die, the cost for die and punch increases. In addition, manufacturing a die and a punch for fine parts is difficult structurally, and this method is inadaptable to products to be manufactured by piercing.